In recent years, efforts have been made toward practical use of a technique for recognizing a measurement target that is measured by a spectral sensor and exists in the surrounding environment of the spectral sensor from multispectral data including a visible light region and an invisible light region, and providing various kinds of support in accordance with the recognized measurement target or its state. For example, for vehicles such as automobiles, a drive support device has been examined for practical application that recognizes pedestrians or other vehicles that exist in the surrounding traffic environment of the vehicle based on spectral data measured by a spectral sensor mounted on the vehicle, and supports driving or decision-making of the driver.
Since spectral sensors are designed to measure a spectrum of a reflected light reflected on a measurement target, the spectrum measured by a spectral sensor is directly affected by the spectrum of ambient light radiated to the measurement target. Such ambient light includes solar light and illumination light, which radiates to the measurement target. The spectrum of the ambient light varies under influence of the weather, the brightness around the measurement target, and objects and the like that exist around the measurement target. Therefore, in order to recognize a measurement target based on the spectrum of the reflected light, it is difficult to improve accuracy in recognizing the measurement target, unless the influence of the ambient light radiated to the measurement target is taken into consideration.
Therefore, conventionally, techniques for reducing the influence of ambient light included in spectrum of reflected light have been proposed, and Patent Document 1 describes one example. The spectrometer described in Patent Document 1 includes a spectral sensor for measuring a reflected light spectrum of a measurement target for each pixel; a spectral sensor for detecting a measured ambient light spectrum of a target to be measured in a measurement environment, and calculating means for calculating a spectral reflectance distribution of the measurement target from the reflected light spectrum and the measured ambient light spectrum of these measurement targets. Further, the spectrometer of Patent Document 1 includes a spectral sensor for detecting a reproduced ambient light spectrum in a reproduction environment, spectrum converting means for converting the measurement target to a spectrum at the time of measuring it based on the reproduced ambient light spectrum, and reproducing means for reproducing the converted spectrum. Thus, an influence of the measured ambient light spectrum included in the reflected light spectrum of the measurement target can be removed, and the influence of the reproduced ambient light spectrum can be taken into consideration. Accordingly, the colors of the measurement target measured in the measurement environment can be reproduced with fidelity.